Electrical connector



Dec. 10, 1957 K. M. HAMMELL ELECTRICAL CONNECTOR Filed Dec. 29, 1953 United States Paten ELECTRICAL CONNECTOR Kemper M. Hammell, Harrisburg, Pa., assignor to A M P Incorporated, a corporation of New Jersey Application December 29, 1953, Serial No. 400,996

12 Claims. (Cl. 339273) This invention relates to self-locking electrical terminals and particularly to taper pins and/or tabs of small size made from sheet metal.

The provision of electrical connections in electrical equipment has long needed small connections which can be easily made and disconnected even where space is limited and which will allow satisfactory connections very close together.

It is an object of this invention to provide a simple and practical terminal connector, connector-receptacle and connection free from adjustable parts, of low electrical resistance and having, when necessary, high current carrying capacity. It is a further object to provide a terminal connection of the character described, the parts of which may be brought together with relatively light force; but which will have ample resistance to pull out forces and vibrations.

Other objects and advantages will be in part obvious and in part pointed out hereinafter. To this end, the present invention consists in the novel features of construction, arrangements of parts and combinations of elements shown herein and more particularly described and pointed out in the attached claims.

In the accompanying drawings there is shown several examples of the invention and I shall describe below these and various modifications and alternatives; but it is to be understood that these are not, and are not intended to be, exhaustive or limiting of the invention but on the contrary are given in order to best illustrate the invention and to instruct others skilled in this art in the principles of the invention and of its application to practical use that they may be enable to understand it fully and to modify and adapt it to the conditions and requirements of varied uses.

In these drawings:

Figure 1 shows a perspective view of a taper pin connector embodying the present invention, in operative rela tion to a tapered receptacle shown in section;

Figure 2 is an exploded and enlarged perspective view of a fiat taper pin connector and a taper receptacle for the connector;

Figure 3 is a section of insulation panel having a taper eyelet mounted therein for the reception of a connector of the type shown in Figure 1;

Figure 4 is a sectional perspective view showing a plurality of tubular sheet metal receptacles for taper pins suitably mounted in an insulation block;

Figure 5 shows the end view of a tubular receptacle;

Figure 6 is a plan view of a portion of metal strip comprising a plurality of taper receptacles arranged in ladder formation; and

Figure 7 is a side view in elevation of the receptacle of Figures 4 and 5 receiving therein the taper pin connector of Figure 1.

The same reference characters indicate like parts. Referring to Figure 1 the connector comprises a taper pin portion 1 and a ferrule portion 2 connected to the base of the taper pin by a neck portion 3 formed as an out wardly projecting bead extending around the circumference of the pin base. The finished article is made from a strip of conductive metal, as brass, which has been formed in a sheet metal stamping operation, or otherwise, so that the width of the terminal-forming strip narrows from the ferrule end of the pin to its tip, to provide a uniform taper when the strip has been rolled to its rounded form with the converging edges in substantial abutment. Preferably the connector is plated with a metal of a more plastic character than the base sheet metal, such as tin, silver or gold, by electro-plating techniques well known in the art.

In the drawing the numeral 4 indicates a section of a receptacle for the pin having a reamed taper conforming to the taper of the pin, as shown at 5 which receptacle, if desired, may be similarly plated as the pin.

Referring to Figure 2 a portion of a flat taper pin 10 is shown which conforms in shape to the taper included between the sides 11 of the tab receptacle 12. In this figure a ferrule 13 integral with the tab receptacle is shown crimped to a wire 14. Pin 10 and receptacle 12 may be provided with an electro-plated coating thereon, if desired. 7 I

In attaching the ferrules 2 and 13 of pin 1 and receptacle 12 respectively to the bared ends of insulated conductors, the connectors are advantageously formed in continuous strips and wound on reels so as to be applied by automatic or semi-automatic connector applicator machines as disclosed, for example, in the copending application to Quentin Berg, Serial Number 151,795, filed March 24, 1950, now Patent 2,778,097 issued January 22, 1957. Thus a plurality of connectors 12 may be left, in the blanking and forming operations, with linking strips 17 joining the connectors in a ladder-like arrange ment, as shown in Figure 6, the pre-applied ferrule 13' having upstanding ears adapted to be received and curled around the conductor as illustrated in Figure 2. In the applicator or crimping operation, the wire strands of the conductor are gathered with the ferrule and strands being pressed into a pre-determined volume while linking strips 17 are severed from the connector. The taper pins are preferably rolled from strip stock to very close tolerances and wound end-to-end on reels, readily usable with the aforesaid applicator machines.

The use of taper pins with tubular receptacles or sockets such as are shown in Figures 4 and 5 has been otherwise mentioned herein. Eyelets such as is indicated by the numeral 15 in Figure 3 permit the satisfactory use of taper pins for connection in thin sheet metal, printed circuits, etc.

The pin connectors described herein and shown in the drawings, as commonly employed, have a taper angle (i. e., the angle included between opposite surfaces of the tapered pin) from about 3 to about 4. Beyond these limits it is generally better to increase the angle beyond 4 than to reduce it below 3. From a theoretical standpoint, the optimum angle will depend upon coefficients of friction of the surfaces of the pin and the receptacle into which it is inserted, but as a practical. matter, a metal taper pin having a taper less than about 7 may be regarded as a self-locking pin, if properly inserted. The metal used for the body of the pin and in plating, if any, or other treatments of its surface, the physical character of the surface, and the amount of force used for insertion of the pin into its receptacle, all become more important as the angle is increased beyond 4 or reduced below 3. The wider the angle becomes, the less the friction between the pin and the receptacle, the greater the axial component of force tending to loosen the pin, the less secure is the locking of the taper, and therefore the less reliable the conductivity and the contact resistance of the connection. (3n the other hand, the smaller the taper angle, the farther the pin will have to be inserted to come home into solid locking relation with a given gripping force. Consequently, the more important the friction during insertion becomes, because a given energy applied for insertion of a pin may be consumed in friction before the pin is properly driven home sufiiciently solidly to give a desired low contact resistance. Moreover, because sliding friction is lower than static friction, the theoretical force required to pull out the taper pin when fully inserted is greater than the force required for insertion. I have found, therefore, that with the very small tapers there is more serious variation both in contact resistance and in pullout resistance, depending upon the manner of insertion and energy exerted, than with the taper having an angle of 3 or 4, especially 3.5", made in accordance with the present application.

The larger the included angle, the less variable becomes the depth of insertion of the pin because of variations in tolerance. It is obvious that if there were no taper on the pin, the pin might be inserted infinitely far in a uniformly cylindrical socket. As presently constructed, with an angle of about 3.5 it has been found that a variation of one thousandth of an inch (0.001) in diameter of the pin means a variation of something like fifteen thousandths of an inch (0.015) in the extent or depth of insertion of the pin in its socket. The smaller the taper angle the greater the variation in extent of insertion resulting from variations within a given pin diameter tolerance.

The receptacles 19 shown in Figures 4 and are made from a strip of beryllium copper about ten thousandths of an inch (0.010) in thickness, the receptacle portions 20 being rolled to cylindrical form. The cylinders are supported in a phenolic resin block 21 provided with a cover plate 22 and when a taper pin is inserted into the cylindrical receptacle the latter is fiexed somewhat into a conical configuration conforming at least in part to the outer surface of the pin as shown in Figure 7.

It has been found that electrical conductivity may be satisfactory if a point or ring contact is made somewhere along the length of the pin. From security standpoints, however, it is desirable that contact be made at least in two ring areas extended axially at least a distance equal to one and one-half times the pin diameter to prevent wobbling of the pin if subjected to the action of lateral forces.

A very great advantage found with connectors made in accordance with this invention is that they fail safe, i. e., whereas with ordinary electrical connectors use and wear tend to loosen the connection and reduce the contact resistance, it is found that these connectors, when subjected to repeated use, vibration, or conditions of corrosion, are more securely connected and ordinarily maintain or decrease their low contact resistance. Thus, the worst that can happen from ordinary failure in the connection is that it cannot be as readily disconnected as it could have been when first put into use.

The simplicity and unusual characteristics of these connectors make them useful in a Wide range of applications. Primarily they are intended to be connectors for individual wires. They can be used to make permanent connections or as disconnects because they are easily sepa rated and reinserted without special tools. Because they remain secure under severe vibrations, they find ready use for attaching wires to multiple connector plugs and relays. Taper receptacles of the tab variety are used widely on spaced relay switch and socket tabs.

It will be seen from the foregoing that the invention is one well adapted to attain the ends and objects hereinbefore mentioned in a practical and efficient manner.

I claim:

1. A self-locking frictional engaging connector comprising a pin portion and a ferrule portion integral therewith for cold-forging onto an electrical conductor, said pin and ferrule portions being formed from sheet metal, said pin portion being formed with lateral edges con- 4 verging toward the end thereof remote from the ferrule portion and into a uniform cross section with the converging edges providing a uniformly tapered pin, and a conductive coating of tin on said pin portion.

2. A self-locking frictional engaging connector comprising a pin portion anda ferrule portion integral therewith for cold-forging onto an electrical conductor, said pin and ferrule portions being formed from sheet metal, said pin portion being formed with lateral edges converging toward the end thereof remote from said ferrule portion, with said converging edges being brought substantially into abutting relation to provide a hollow uniformly tapered pin, and a conductive coating on said pin portion of a metal of more plastic character than said sheet metal.

3. A self-locking frictional engaging connector comprising a pin portion and a ferrule portion integral therewith for cold-forging onto an electrical conductor, said pin and ferrule portions being formed from sheet metal, the pin portion being formed with lateral edges converging toward the end remote from the ferrule with said converging edges brought into substantial abutting relation, thus providing a hollow uniformly tapered pin, the taper of said pin portion being from 3 to 7.

4. A self-locking connector as in claim 3 in which the taper of each said pin portion is approximately three and one-half degrees.

5. A connector as in claim 1, in which the sheet metal is formed to the shape of a flat tab having uniformly converging lateral edges.

6. A connector as in claim 1, in which the sheet metal is formed to rectangular cross section and in which lateral edges converge uniformly.

7. An electrical connection which comprises a taper pin having a taper from 3 to 7 and a receptacle having a hole, the inner surface of which is at least in part an electrical conductor, a part of said hole being of lesser diameter than the broadest part of the taper on said pin, and the mouth of said hole being wider than the outer end of the pin, the material of said receptacle being adapted to expand resiliently so as to engage the taper pin in substantial surface conformity therewith, at least at the extremities of a band equal in breadth from 1 /2 to 2 /2 times the diameter of the taper pin, said receptacle gripping the pin with substantial resilient force resulting from distortion of the receptacle by action of the taper and holding the pin against axial withdrawal by surface friction resulting from said grip.

8. An electrical connection which comprises a taper pin having a taper of 3 /2 and a receptacle having a hole, the inner surface of which is at least in part an electrical conductor, a part of said hole being of lesser diameter than the broadest part of the taper on said pin, and the mouth of said hole being wider than the outer end of the pin, the material of said receptacle being adapted to expand resiliently so as to engage the taper pin in substantial surface conformity therewith, at least at the extremities of the band equal in breadth from 1 /2 to 2 /2 times the diameter of the taper pin, said receptacle gripping the pin with substantial resilient force resulting from distortion of the receptacle by action of the taper and holding the pin against axial withdrawal by surface friction resulting from said grip.

9. A taper pin as claimed in claim 1 wherein surface portions comprise a porous, electro-tinned coating.

10. An electrical connection comprising a pin formed from sheet metal having lateral edges converging toward one end thereof, said edges being brought into substantial abutting relation to provide a hollow uniformly tapered pin, and a receptacle receiving said pin and having a contact surface tapered in accordance with the taper of said pin, the engaging surfaces of said pin and receptacle having a conductive electro-deposited plating thereon.

11. A self-locking frictional engaging connector comprising, in combination, a sheet metal pin portion and an integral sheet metal ferrule portion adapted to be coldforged onto a wire, said pin portion being formed with lateral edges converging toward the end remote from the ferrule with said edges being brought into substantial abutting relation to provide a hollow uniformly tapered pin, an outwardly projecting circumferential bead between said pin and ferrule portions, and an electroplated conductive coating on at least said pin portion.

12. A self-locking frictional engaging connector comprising a sheet metal pin portion and an integral sheet metal ferrule portion for cold-forging onto an electrical conductor, said pin portion being formed with lateral edges converging toward the end thereof remote from the ferrule with said edges being brought substantially into abutting relation to provide a hollow uniformly tapered pin, and outwardly projecting and circumferentially extending bead between said pin and ferrule portions, and a conductive coating on at least said pin portion.

UNITED STATES PATENTS Blake NOV. 15, 1881 Danley July 7, 1914 Boothman Apr. 15, 1924 Bjorndal Nov. 3, 1931 Berndt Apr. 17, 1937 Siegmund Sept. 1, 1942 Batcheller June 10, 1952 FOREIGN PATENTS Great Britain May 21, 1925 OTHER REFERENCES Publication: Electrical Mfg, August 1953. 

